[petsc-users] Problems with preconditioners, which one?

[Barry Smith]

  Is this coming from a Stokes-like problem? 

  Barry


On Aug 3, 2010, at 10:54 PM, Filippo Spiga wrote:

> Dear Hong,
>> This confirms that your Jacobian is singular, thus none of linear
>> solvers would work.
> 
> So do any preconditioner not help me to solve the problem?
> 
> I put some stuff here: http://tinyurl.com/fil-petsc
> - "A_LS.m" is matrix (saved by PETSc)
> - "b_LS-m"
> - the file "eigenvalues_A" contains the eigenvalues of the matrix A, computed by MATLAB.
> 
> I used "-pc_type lu" and 1 only processor. The result is the same of my previous email (*).
> 
> Anyway if I solve the problem using MATLAB I get the right solution. The formulation seems correct. To be honest, the eigenvalues don't say me nothing. But I'm a computer scientist, not a mathematician. I'm not able to recognize which preconditioner I should use or which modifications (scaling all/part of the rows? reformulate the system in another way?...) do to solve the problem. From my side, it is not possible to try all the preconditioners and also it is not the right way...
> 
> Once again, thanks.
> 
> (*)
> [0|23:14:58]: unknown: MatLUFactorNumeric_SeqAIJ() line 668 in src/mat/impls/aij/seq/aijfact.c: Zero pivot row 1 value 0 tolerance 2.77778e-14 * rowsum 0.0277778
> 
> -- 
> 
> Filippo SPIGA
> 
> «Nobody will drive us out of Cantor's paradise.»
>     -- David Hilbert
>